The term "seat unit" is defined as any part of a vehicle seat which has at least two seat elements. Seat elements means all elements which belong to the structural and/or functional design of a vehicle seat including fixing and adjusting mechanisms. In particular, two rail devices for longitudinally adjusting the seat are seat elements.
From DE 37 03 515 A1 a seat unit is known where a bearing on the floor side has upper and lower rails whereby the seat can be moved forwards and backwards. The seat frame supporting a seat cushion is connected to the separated upper rails of the bearing by guide rods which are provided in the front and rear areas of the seat. Apart from longitudinally adjusting the seat, smooth-changing gears allow the height of the seat, as well as the incline of the seat, to be adjusted. These gears are fitted on the seat frame. The disadvantage with this construction is the number of individual structural elements which have to be fixed on the upper rail. This leads to relatively high production costs.
In DE 44 19 139 a device is disclosed in which the number of structural parts on the upper rail is limited. To this end, a frame construction is provided for the seat of a vehicle with a seat surface part, a backrest part and support parts for supporting the seat surface part on a rail structure mounted on the vehicle floor in the longitudinal direction of the vehicle. The support parts are formed in one piece as aluminum extruded pressed profiled parts with structural elements running in the longitudinal direction of the vehicle. Bulges are formed crosswise to the profiled plane to reinforce the profiled part against bending around an axis parallel to the longitudinal direction of the profile.
With this proposal the number of structural elements required for fixing the seat on the rail structure is reduced, however, all the additional elements (e.g., guides and gears for a longitudinal and height adjustment of the seat) must also be additionally fixed on the frame structure. Indeed, the fixing means for the individual structural parts (e.g., bores or milled areas) must generally be made by a second work step which takes place after the extrusion pressing.
From DE 94 12 155.9 U1 a rail guide is known which has two relatively displaceable rails in which one rail supports plastics-coated teeth extending along the displacement path into which a drive worm connected to the other rail engages through further gearing elements. The outer contour of the plastics-coated teeth, which consists of toothed elements or a toothed rod, corresponds to the contour of the engagement area of the drive worm teeth which are formed as inclined teething. The plastics-coating straight teeth, made by punching, can be converted into inclined teeth to produce a permanent surface contact with the worm.
A disadvantage with this solution is the expensive manufacture and number of work steps required to produce the inclined teeth.
From DE 196 17 877 A1 a rail guide is known which comprises two rails which can be displaced relative to each other in the longitudinal direction, and a gear housing connected to one of the rails by fixing means. In detail, a gear housing, connected to the first rail, is displaceable across the longitudinal direction of the rails for the purpose of adjusting play in the seat and can be locked in a position where the teeth of one displacement worm mounted in the gear housing engages with the teeth of the second rail. With this solution the two separate elements (gear housing and rail) have to be connected together by a separate fixing means which is a disadvantage.